1. Field of the Invention
The subject invention relates to printing equipment and more specifically, to wrap-on printing plate systems, structures and assemblies.
2. Information Disclosure Statement
Rotogravure printing is becoming increasingly preferred over offset printing where high printing printing quality is important, especially for long printing runs. Rotogravure printing also turns out to be more economical than offset printing, when high quality is to be maintained throughout extremely long runs.
However, unlike offset printing, rotogravure printing has lacked flexibility. In this respect, recent years have seen an increasing demand for items of regional interest and for local advertisements in national newspapers and periodicals. This demand has been paralleled by an increasing need for effective language or text changes, or listings of such items as prices and firm names, in larger, otherwise unaltered catalogs or other texts. These and other changes in copy, page insertions and regional advertisements are costly to the gravure printer in production time and expense.
A solution to this problem has been seen in providing a rotogravure system with exchangeable printing plates which may be wrapped onto the printing cylinder so as to permit localized changes to be effected thereon without replacement of an entire printing cylinder. The term "wrap-on" is employed herein generically, to extend at least to wrap-around plate systems and to systems in which the printing plate is only wrapped on part of the form cylinder.
Such wrap-on printing plates form elements, as for instance known from my U.S. Pat. No. 4,157,067, issued June 5, 1979, and its corresponding German Patent Publication, DE-OS No. 28 04 304, should be as thin as possible for weight saving reasons and particularly so as to be clampable evenly onto the printing form cylinder and to fit everywhere tightly onto that form cylinder. In addition, care must be taken that the butt joints between clamped-on printing plates are as closed or tight as possible in the axial direction as well as in the circumferential direction of the printing form cylinder, so that practically no printing ink can intrude the butt joints and be deposited there.
In my above mentioned U.S. Pat. No. 4,157,067, including FIGS. 8, 9 and 10 thereof, a seal for the circumferential butt joints has been previously proposed by either a canting of the printing plates at their side edges in order to form a hollow space for the reception of a seal, or by providing slots in the printing cylinder in which seals are installed. In practice, such constructions are expensive from a production point of view and the seals used therein require maintenance.
In addition, as shown with the aid of FIG. 7 of my above mentioned U.S. Pat. No. 4,157,067, I have tried to provide the side edges of wrap-on printing plates with sealing surfaces and to attain a sealing of the butt joints by joining the sealing surfaces of adjacent wrap-on printing plates tightly together. However, in extensive printing operations, such a solution was not able completely to avoid the deposit of printing ink in the butt joints because a continous tight contact of the sealing surfaces of the adjacent wrap-on printing form elements cannot be guaranteed throughout the printing process. In practice, such ink deposits leave undsirable marks on printed products.
Reference may also be had to my U.S. Pat. No. 4,437,942, issued Mar. 20, 1984, and disclosing methods and apparatus for producing wrap-on printing plates with clamping bars, and such printing plates produced by such methods and apparatus.